1. Field of the Invention
The present invention is related to a stereo signal generator, and particularly to a stereo signal generator which can add a stereophonic sound field effect to a monaural sound signal.
2. Description of the Prior Art
Conventionally, in systems such as electronic musical instruments, loudspeaker systems and audio systems, in which musical tones or the like are generated from the left and right speakers, a technique of varying the ratio of sound volume levels of musical tones generated from the left and right speakers has been used as the method for controlling the localization (pan-pot, pan effect) of a sound source.
FIG. 3 is a block diagram showing the main portions of the conventional localization control circuit. A monaural sound input signal I is supplied to two multipliers 30 and 31, and control signals CR and CL are respectively supplied to each multiplier. These control signals CR, CL are adjusted so that one increases as the other decreases. Multipliers 30 and 31 multiply the input signal I by the respective control signals CR, CL and provides a right output OR and a left output OL, respectively. In the conventional system, the localization of a sound source is controlled by appropriately selecting these control signals.
The human ears are positioned at the left and right sides of the head, and for Instance, a sound reaching from the right-hand side directly reaches the right ear, but it reaches the left ear while going around the head. As the general nature of sound, tile level of a sound going around to tile back of an obstacle lowers by diffraction as the frequency increases.
Accordingly, for a sound coming from the right-hand side, the sounds listened by tile right and left ears are different not only in tile volume level but also in the frequency characteristics. On the other hand, in the system in which musical tones or the like are provided from two, that is, left and right speakers, tile sounds generated from the left and right speakers directly reach the left and right ears, respectively. This is more remarkable in headphones or carphones.
In these systems, since the localization is controlled only by changing the volume balance, the frequency characteristics of the sounds generated from the left and right speakers are different from those of the sounds reaching the ears from a natural sound source, and thus there has been a problem that the localization is unnatural and presence or ambience is poor.